1. Field of the Invention
The present invention relates to an information system having multiple access and a decentralized exchange, and more particularly to such a system having a tree-type conductor network comprising branches, branch points or nodes and stations, in which each branch consists of two paths of mutually opposite transmission directions, all paths in the network having the same number of transmission channels and each channel of a path being associated with a channel of the other path of the same branch to provide a channel pair, with each channel pair of a branch being oppositely and clearly associated with a channel pair of each adjacent branch in the network so that a channel pair tree is produced and each station is connected to both paths of a branch and does not delete arriving signals, but only reads such signals.
2. Description of the Prior Art
In an information network having decentralized exchange operation, a station can establish a connection with a desired other station entirely independently. For this purpose, the station must be independently able to receive messages from the information flow of a common transmission medium, or feed in, respectively. Each station must control all channels in the common transmission medium. Time multiplex technology is particularly suited for the realization of the above, since, in comparison with frequency multiplex technology, parallel control units can be omitted and essentially less band width is required, as compared with code multiplex technology.
Heretofore, loop conductor networks have primarily been discussed for such information networks operating on the decentralized principle. See, for example, the German published application No. 1,925,604. In a loop network, a single transmission direction is required and, for connection between two stations, only one transmission channel is necessary within the loop. Loop conductor networks, however, have the drawback that they can only be expanded with difficulty; furthermore, measures must be taken for preventing circulation of information blocks several times within the network which would cause blocking of the transmission path. This also renders the transmission from one loop to another more difficult.
In a tree-type conductor network, i.e. a conductor network which is designed without meshes, these drawbacks are avoided. However, each branch of such a network must consist of two paths having opposite transmission directions. A tree-type conductor network having time multiplex transmission technology has been described by Schenkel within the framework of the 1974 International Zurich Seminar on Digital Communication, wherein each double conductor of each network branch is subdivided into a transmitting line and a receiving line having opposite transmission directions, and each participant station is connected with the transmitting line and the receiving line of its network branch, whereby it transmits its information only upon the transmitting line and receives information directed thereto only on the receiving line. Received information is thereby not taken out of the flow of information, but is recognized when it passes the station. All receiving lines are connected with each other in each network node, and also all transmitting lines are similarly connected. At the end of only one branch, called network end A, the transmitting line is connected with the receiving line in order to supply the sum of all messages transmitted within the network to all participant stations, via the receiving lines. Therefore, all participant stations are also familiar with the occupation pattern of the time slots at the position of the greatest traffic flow. A timing generator at the end of another branch transmits synchronization blocks, periodically, upon the transmitting line of this branch. This synchronization information travels toward the network end A and, from there, to all participants via the receiving lines. Since each participant station must be synchronized with the time multiplex framework used for the information transmission, not only upon the receiving line but also upon the transmitting line, but the synchronization information is not present upon a number of transmitting lines, the synchronization information of the receiving line is received there at the end of the network branch, and it is delayed and fed to the transmission line. The delay in each of those network ends is selected in such a manner that the transit time from the network end via the point at which the receiving line and transmitting line are connected with one another, back to the same network end is supplemented to become an integer multiple of the duration of a time multiplex frame. Thereby, the entire network is in frame synchronism.
As compared with a loop conductor network, however, the messages transmitted by both participants must be transmitted upon each path, in the case of the tree-type conductor network. For this purpose, two channels are required for each connection upon both paths of each branch. In the case of an even arrangement of the stations upon a squared range, this will result in approximately four times the transmission expense, technically, in a case of an equal traffic load, as compared with loop conductor networks.